First Article Inspection: Why You Can't Afford to Skip It

What Is First Article Inspection?

First article inspection (FAI) is the practice of thoroughly measuring the very first part that comes off the machine after a setup. You check every critical dimension. You compare it to the drawing. If it's good, you run the batch. If it's not, you stop, find the problem, fix it, and run another first article.

It's not a quick glance with a caliper. It's a systematic check. You need a checklist. You need the right gauges. You need to record the results.

For production runs, there are formal standards like AS9102 for aerospace. But even for a simple job shop part, you need a process.

Why It's So Important

It catches setup errors. Did you pick the right tool? Is the work offset correct? Did you use the right fixture? These mistakes happen. They happen to everyone. A first article check catches them before you make a hundred bad parts.

It verifies the program. Maybe the program is wrong. Maybe the post-processor introduced an error. Maybe someone edited it since the last run. The first article tells you if the program is making the part you intended.

It confirms tooling and workholding. Is the part moving? Is the tool deflecting? Is the surface finish acceptable? These things aren't obvious from looking at the code. You have to run a part and check it.

It documents the process. If you record the first article measurements, you have a baseline. When you run the job again next month, you can compare the new first article to the old one. If something is different, you know something changed.

It saves money. The cost of inspecting one part is tiny. The cost of scrapping a batch of 500 parts is huge. First article inspection is cheap insurance.

How to Do a Proper First Article

You don't need a CMM for every part. But you do need a plan.

Create a checklist. List every dimension that matters. Include tolerances. Include notes about how to measure (e.g., "use bore gauge, not calipers"). I keep a template in my shop that I fill out for each job.

Use the right tools. Calipers for rough dimensions. Micrometers for tight tolerances. A bore gauge for holes. A height gauge for locations. A surface plate and indicator for flatness. A thread gauge for threads. Don't guess.

Check the critical features first. The features that are hardest to hold, or that have the tightest tolerances, should be checked before anything else. If they're bad, stop immediately. Don't waste time checking non-critical dimensions.

Check at the machine or in inspection? I prefer to do the first article at the machine, with the part still in the fixture. That way, if something is wrong, I can adjust offsets or change tools without disturbing the setup. But for complex parts, I may take the part to the inspection room for a more thorough check.

Record the results. Write down the measured values. Keep them in a job folder. If the customer asks for a first article report, you have it. If the job runs again, you have a reference.

Get sign-off if required. For aerospace, medical, or automotive work, the customer may require their own approval of the first article. Build that time into your schedule.

What to Check

Not every dimension needs the same level of attention. Focus on:

• Critical-to-function dimensions. The ones that affect fit, assembly, or performance. Usually these have tight tolerances or are called out with GD&T.

• Locations of holes and features. These are easy to get wrong if work offsets are off.

• Threads. A bad tap or wrong drill size can ruin a thread. Check with a go/no-go gauge.

• Surface finish. If the drawing calls out a specific Ra, measure it. Don't just look at it.

• Datum references. The first article should be set up on the datums as specified on the drawing. Not just any edge.

• Material and heat treat. Verify that the material is correct and that any heat treat or coating was done properly.

For dimensions that are non-critical (like a clearance hole that's ±0.5mm), you can skip them or just do a quick visual check. Focus your time where it matters.

Common First Article Mistakes

Measuring the part in the fixture. If the part is clamped, it might be distorted. Measure it in a free state unless the drawing specifies otherwise.

Using uncalibrated tools. A micrometer that reads 0.02mm off will cause you to chase phantom errors. Calibrate your tools regularly.

Not measuring enough points. One measurement on a bore might miss a taper. Measure at the top, middle, and bottom.

Ignoring the datum structure. The part must be measured relative to the datums called out on the drawing. If you set it up differently, your measurements are meaningless.

Assuming the first part is good. The first part could be bad. That's why you inspect it. Don't assume.

When You Find a Problem

You measured the first article and something is wrong. Now what?

Stop. Don't run any more parts. Don't try to adjust on the fly. Stop and figure out what's wrong.

Identify the root cause. Is the tool worn? Is the work offset wrong? Is the fixture loose? Is the program incorrect? Don't just tweak an offset and hope. Find the real cause.

Fix it. Change the tool. Reset the offset. Tighten the fixture. Edit the program. Then run another first article.

Don't skip steps. If you fix one problem, you might create another. Check everything again.

Document the issue. Note what went wrong and how you fixed it. That knowledge will help you avoid the same mistake next time.

First Article for Prototypes vs. Production

For a one-off prototype, the "first article" is the only article. You still need to inspect it thoroughly to make sure it meets the drawing. But you don't need to worry about batch consistency.

For production, the first article is the baseline. If it's good, you can run the batch. But you still need in-process checks to catch drift from tool wear or thermal changes.

For high-volume production (thousands of parts), the first article is part of a larger quality plan that includes statistical process control, tool life monitoring, and regular sampling.

A Real Example: A Medical Component

A customer sent me a drawing for a small titanium part. Ten pieces only. Tight tolerances: ±0.01mm on a bore, ±0.02mm on a slot location. I programmed the job, set up the machine, and ran the first part.

I measured the bore. It was 0.008mm undersize. I checked the tool. It was new, but the tool holder had 0.01mm runout. I changed to a hydraulic holder, runout dropped to 0.002mm. Ran another first article. The bore was perfect.

If I had skipped the first article and run all ten parts, nine of them would have been bad. The customer would have rejected the batch. I would have lost the job and possibly the customer.

The first article took 15 minutes. It saved me from scrapping $800 worth of titanium and hours of rework.

What I Tell New Machinists

When a new guy starts in my shop, I tell them this:

"The first article is not optional. It doesn't matter if you're in a hurry. It doesn't matter if you've run this job before. It doesn't matter if the customer is waiting. You will measure the first part before you run the second."

"Assume the part is wrong until you prove it's right. I've seen experienced machinists scrap entire batches because they trusted the setup. Don't be that person."

"If you find a problem, stop and tell me. I won't be mad. I'll be happy you caught it before we made a hundred bad parts."

The Bottom Line

First article inspection is not a bureaucratic requirement. It's a practical necessity. It catches mistakes early, when they're cheap to fix. It builds confidence in your process. It protects you from scrapping hundreds of parts because of one small error.

It takes a few minutes. It costs almost nothing. But it can save you days of rework and thousands of dollars in scrap.

Don't skip it.

What's your worst story about skipping first article inspection? Or the time it saved you? I'd like to hear it.